Rising methane gas bubbles form massive hydrate layers at the seafloor

Extensive methane hydrate layers are formed in the near-surface sediments of the Cascadia margin. An undissociated section of such a layer was recovered at the base of a gravity core (i.e. at a sediment depth of 120 cm) at the southern summit of Hydrate Ridge. As a result of salt exclusion during methane hydrate formation, the associated pore waters show a highly elevated chloride concentration of 809 mM. In comparison, the average background value is 543 mM.A simple transport-reaction model was developed to reproduce the Cl⁻ observations and quantify processes such as hydrate formation, methane demand, and fluid flow. From this first field observation of a positive Cl⁻ anomaly, high hydrate formation rates (0.15-1.08 mol cm⁻² a⁻¹) were calculated. Our model results also suggest that the fluid flow rate at the Cascadia accretionary margin is constrained to 45-300 cm a⁻¹. The amount of methane needed to build up enough methane hydrate to produce the observed chloride enrichment exceeds the methane solubility in pore water. Thus, most of the gas hydrate was most likely formed from ascending methane gas bubbles rather than solely from CH₄ dissolved in the pore water.     

Constitutive modeling of cyclically loaded clays with entrapped gas bubbles under undrained and unexhausted conditions

Acta Geotechnica - Fine-grained gassy marine sediments are widely distributed around the world, and the cyclic behavior of this type of sediments has a great influence on the foundations of...     

Laboratory studies on eelgrass seed and seedling predation

Ten species, including crustaceans, molluscs and fish, were examined for predacious activity onZostera marina L. seeds and seedlings. Predation was examined initially by offering seeds or seedlings as a sole food source for a maximum period of one week. Species exhibiting predation of 10% or more of the seeds or seedlings were tested further with bits of clam or scallop as an alternative food source. In these experiments, animals were tested in each of three conditions: 1) alternative food plus seeds or seedlings; 2) alternative food alone; 3) seeds or seedlings alone. In the initial experimentsOvalipes ocellatus, Pagurus longicarpus, andPanopeus herbstii preyed on seeds, andIlyanassa obsoleta, Littorina littorea, andP. longicarpus preyed on seedlings. Limited predation occurred, however, when these animals were presented with seeds or seedlings plus an alternative food. These data suggest that several common crab and snail inhabitants of eelgrass meadows are capable of preying on eelgrass seeds and seedlings, but that this activity may be influenced by the availability of an alternative food source.     

Segregating gas from melt: an experimental study of the Ostwald ripening of vapor bubbles in magmas

Diffusive coarsening (Ostwald ripening) of H₂O and H₂O-CO₂ bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems. Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening is faster in experiments saturated with pure H₂O than in those with a CO₂-rich mixed vapor probably due to faster diffusion of H₂O than CO₂ through the melt. None of the experimental series followed the time^1/3 increase in mean bubble radius and time⁻¹ decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates micron-sized bubbles and would produce mm-sized bubbles in 10²–10⁴ years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles sufficiently large for rapid ascent.     

油酸钠浮选锂辉石的作用机理研究

通过浮选实验、Zeta电位测量和红外光谱分析研究了油酸钠捕收剂体系中锂辉石的浮选行为和作用机理。浮选结果发现,当油酸钠用量为200 mg/L,pH=8⁹时,锂辉石最大浮选回收率为27%;当加入的活化离子Fe3+浓度为35 mg/L时,浮选回收率高达90%,可见Fe3+活化效果显著。Zeta电位测量结果显示锂辉石的零电点约为pH=3.0,加入阴离子捕收剂油酸钠后锂辉石Zeta电位整体向负移,则两者之间存在非静电作用力。在最佳浮选pH值=89时,锂辉石最大浮选回收率为27%;当加入的活化离子Fe3+浓度为35 mg/L时,浮选回收率高达90%,可见Fe3+活化效果显著。Zeta电位测量结果显示锂辉石的零电点约为pH=3.0,加入阴离子捕收剂油酸钠后锂辉石Zeta电位整体向负移,则两者之间存在非静电作用力。在最佳浮选pH值=8⁹时,锂辉石Zeta电位变化最显著,表明此时发生的吸附作用最大。结合红外光谱测试结果可得出结论:油酸钠在锂辉石表面吸附主要通过化学作用。     

Dynamics of bubbles in supernovae and turbulent vortices

We consider the motion of a bubble in a central acceleration field created by gravity or a centrifugal force. In the former case, the bubble moves outwards from and, in the latter, towards the center. We have calculated the characteristic time needed for a bubble to leave or reach the center. The solution obtained provides insight into the processes of thermonuclear supernovae and combustion; in other words, into the interaction between a flame and a turbulent vortex. In the case of combustion, a light bubble of burnt material propagates towards the axis of a strong turbulent vortex faster than it drifts in the direction of rotation of the vortex. It is expected that the development of bubbles should prevent the formation of “pockets” at the flame front, similar to those predicted by a simplified model of turbulent combustion in a constant density flux. In the case of a thermonuclear supernova in a deflagration burning regime, it is shown that light products of burning rise from the center of the white dwarf substantially more rapidly than the thermonuclear flame front propagates. As a result, a flame cannot completely burn the central part of the star, and instead is pushed to the outer layers of the white dwarf. The effect of bubble motion (large-scale convection) makes spherically symmetric models for thermonuclear supernovae unrealistic, which is of prime importance for the supernova spectrum and energy. The motion of bubbles is even faster in the case of a rotating white dwarf; under certain conditions, the centrifugal force may dominate over the gravitational force. To test this theory, we have carried out numerical simulations of supernovae explosions for various sizes of the burned region in the core of the presupernova. We have derived a relation between the rate of large-scale convection and the size of the burned region, which is specified by the rate of the deflagration in the thermonuclear burning.     

Genetic diversity and structure of natural and transplanted eelgrass populations in the Chesapeake and Chincoteague Bays

The objective of this study was to gain baseline population data on the genetic diversity and differentiation of eelgrass (Zostera marïna L.) populations in the Chesapeake and Chincoteague bays. Natural and transplanted eelgrass beds were compared using starch gel electrophoresis of allozymes. Transplanted eelgrass beds were not reduced in genetic diversity compared with natural beds. Inbreeding coefficients (F_IS) indicated that transplanted eelgrass beds had theoretically higher levels of outcrossing than natural beds, suggesting the significance of use of seeds as donor material and of seedling recruitment following transplantation diebacks. Natural populations exhibited very great genetic structure (F_ST=0.335), but transplanted beds were genetically similar to the donor bed and each other. Genetic diversity was lowest in Chincoteague Bay, reflecting recent restoration history since the 1930s wasting disease and geographical isolation from other east coast populations. These data provide a basis for developing a management plan for conserving eelgrass genetic diversity in the Chesapeake Bay and for guiding estuary-wide restoration efforts. It will be important to recognize that the natural genetic diversity of eelgrass in the estuary is distributed among various populations and is not well represented by single populations.     

Growth of disk-shaped bubbles in sediments

Disc-shaped methane bubbles, often observed in marine sediments, result from growth in a medium that elastically resists expansion of the bubbles and yields by fracture. We have modeled this process to obtain estimates of growth times by using a reaction-diffusion model coupled to a linear elastic fracture mechanics (LEFM). For comparison, we also modeled the growth of a constant eccentricity bubble in a nonresistant medium. Discoidal bubbles that grow in sediments that obey LEFM grow much faster than spherical bubbles (two- to fourfold faster for the times and conditions tested here) and become more eccentric with time (aspect ratios falling from 0.3 to 0.03 over 8 d of growth). In addition, their growth is not continuous but punctuated by fracture events. Furthermore, under some conditions, LEFM predicts that bubble growth can become arrested, which is not possible for a bubble in a nonresistant medium, even for nonspherical bubbles. Cessation of growth occurs when the dissolved gas concentration gradient near the bubble surface disappears as a result of the increase in bubble gas pressure needed to overcome sediment elasticity.     

The Role of Flotation Reagents in the Reverse Flotation of Carbonate-Containing Iron Ores

The Influence of pulp pH, dispersants and auxiliary collectors on reverse flotation of carbonate-containing iron ores were explored. Interactions between iron ores and quartz were theoretically analyzed by flotation solution chemistry and DLVO theory. The results indicated that the iron concentrate grade improved sharply when pH increased from 11.0 to 12.0, but changed unobviously when pH was larger than 12.0, which was related to solution chemistry of siderite and interactions among particles. Sodium tripolyphosphate was an effective dispersant and sodium dodecyl sulfate was an effective auxiliary collector of KS-III. Both recovery and grade enhanced by the action of sodium dodecyl sulfate or sodium tripolyphosphate when pH was 12.0.     

Late glacial impacts on dispersal and colonization of Atlantic Canada and Maine by freshwater fishes

Late glacial scenarios of ice retreat and biogeography databases constrain the dispersal routes of obligate freshwater fishes into Atlantic Canada and Maine. Evidence indicates glacial ice covered the present-day mainland and offshore islands at 18,000 ¹⁴C yr before present. Possible refugia for extirpated freshwater fishes were the exposed outer edge of the Grand Banks (east), exposed Georges Bank (south-Atlantic Refugium), and the Mississippi Refugium in the west. It is improbable that the region was recolonized from the offshore refugia. Rather, fishes recolonized from the east via the upper St. Lawrence River valley into the upper Saint John River, Maine (Lake Madawaska) from 11,000 to 12,000 ¹⁴C yr BP. The short period of entry resulted in the low diversity of obligate freshwater species in the region. Lake Madawaska was breached and dispersal continued into the remainder of the region after 8000 ¹⁴C yr BP. By 6000 ¹⁴C yr BP, access routes to the east along low-lying coastal zones were blocked by rising sea levels, which isolated Prince Edward Island, Cape Breton Island, and most probably Nova Scotia. Natural dispersal across the region appeared complete by this time.     

铝土矿选矿尾矿特性

运用X射线衍射、N2吸附实验、扫描电子显微分析、等离子光谱等多种测试方法对铝土矿选矿尾矿特性进行了研究,揭示了尾矿一些不被关注的性质,诸如铁矿物的嵌布粒度、比表面积随煅烧温度的变化、煅烧对尾矿及其中各矿物化学反应活性的影响以及各主要矿物对磷酸根离子的吸附能力等。这些性质可望在研究废水处理、尾矿增白时得到应用。     

细粒锡石浮选工艺研究实践与展望

都龙锌锡多金属矿中的锡石嵌布粒度细,多年来仅采用常规单一的重选工艺回收锡石导致回收率偏低。随着细粒锡石浮选工艺的研究并应用于生产后,实现了细粒级锡石的高效经济回收,同时改善重选分选条件,提高了粗粒级锡石的回收率,锡综合回收率由45%左右提高到55%以上,经济效益显著,具有良好的推广应用前景。     

Flotation and adsorption studies of chalcopyrite with cupferron

Flotation tests were conducted in a Hallimond tube on chalcopyrite, with a collector system of cupferron and fuel oil. The reagent concentration, pH and conditioning time were studied as variables. The necessity of the fuel oil was verified by conducting experiments without it. Contact-angle measurements have been conducted by the captivebubble technique. From the results it was found that fuel oil is necessary to promote adhesion of the conditioned mineral particles to the air bubbles. Adsorption experiments were carried out in a column apparatus under similar conditions as in flotation, except for the addition of fuel oil. The adsorption density and flotability were high at weakly acidic range where the reagent complexes the metal ions effectively in an aqueous medium.     

SF_6气体示踪法测定低透气性高瓦斯煤层瓦斯抽放半径

针对目前应用较多的瓦斯抽放半径测定方法——相对瓦斯压力测定法与实际情况偏差较大问题,以神华乌海能源公司平沟煤矿16号低透气性高瓦斯煤层为研究对象,在井下1606工作面施工瓦斯抽放试验钻孔,采用SF6气体示踪法测定工作面瓦斯的抽放半径,并比较了不同抽放半径的瓦斯抽放效果。实测结果表明,SF6气体示踪法所测定的瓦斯抽放半径使瓦斯抽采效率显著提高,该方法为煤层预抽瓦斯钻孔间距的设计提供了依据,可以在低透气性高瓦斯煤层的瓦斯抽放半径测定中推广使用。     

Subduction, collision and initiation of hominin dispersal

Subduction is the main driving force of plate tectonics controlling the physiography of the Earth. The northward subduction of the Sinai plate was interrupted during the Early Pleistocene when the Eratosthenes Seamount began to collide with the Cyprian arc. A series of synchronous structural deformations was triggered across the entire eastern Mediterranean, and local topography was drastically accentuation along the Levantine corridor – one of the main pathways of hominin dispersal out of Africa. However, the choice of this preferred pathway and timing of dispersal has not been resolved. Though causes for dispersal out of Africa are in debate, we show that the transition from subduction to collision in the eastern Mediterranean set the route.     

Mantle processes during Gondwana break-up and dispersal

This paper reviews the Mesozoic continental flood basalts (CFBs) associated with the break-up and dispersal of Gondwana from 185-60 Ma, the conditions for melt generation in mantle plumes and within the continental mantle lithosphere, and possible causes for lithospheric extension. The number of CFB provinces within Gondwana is much less than the number of mantle plumes that are likely to have been emplaced beneath it in the 300 Ma prior to its initial break-up. Also, the difference between the age of the peak of CFB volcanism and that of the oldest adjacent ocean crust decreases with the age of volcanism during the break-up and dispersal of Gondwana. The older CFBs of Karoo and Ferrar appear to have been derived largely from source regions within the mantle lithosphere. It is only in the younger Paranâ-Etendeka and Deccan CFBs that there are igneous rocks with major, trace element and radiogenic isotope ratios indicative of melting within a mantle plume. These younger CFBs are also clearly associated with hot spot traces on the adjacent ocean floor. The widespread 180 Ma magmatic event is attributed to partial melting within the lithosphere in response to thermal incubation over 300 Ma. In the case of the Ferrar (Antarctica) this was focussed by regional plate margin forces. The implication is that supercontinents effectively self-destruct in response to the build up of heat and resultant magmatism, since these effects significantly weaken the lithosphere and make it more susceptible to break-up in response to regional tectonics. The younger CFB of Paranâ-Etendeka was generated, at least in part, because the continental lithosphere had been thinned in response to regional tectonics. While magmatism in the Deccan was triggered by the emplacement of the plume, that too may have been beneath slightly thinned lithosphere.     

硝酸钠-硫氰酸铵-罗丹明B-水液-固体系浮选分离锌

研究了硝酸钠-硫氰酸铵-罗丹明B-水液-固体系浮选分离锌的行为及其与常见离子分离的条件。结果表明，在NaNO3存在下，NH4SCN—RhB—Zn三元缔合物可浮于盐水相上形成界面清晰的液-固两相，从而使Zn^2 被定量浮选，而Cd^2 、Mn^2 、Al^2 、Ni^2 、Co^2 、Fe%2 等离子不被浮选。应用该方法对合成水样及加碘锌强化营养盐中微量锌进行了定量浮选分离测定，样品标准加入回收率为98．3％-101．8％。